Multidiversity handoff in a wireless broadcast system

ABSTRACT

A wireless broadcast system that collects content for distribution over a wireless communication network. The content stream is encapsulated into a stream of transport packets for broadcast over the wireless communication link. The stream of transport packets are simultaneously broadcast as part of an identical signal from a plurality of synchronized transmitters in a single frequency network. A receiver acquires the broadcast signal and synchronizes to the signal. Once the receiver is synchronized to one of the transmitters in the single frequency network, the receiver can receive signals from any, or multiple, of the transmitters in the network without re-synchronizing.

BACKGROUND

1. Field of the Invention

This invention relates generally to a wireless communication system, andin particular to a wireless broadcast communication system.

2. Background

Wireless communication networks typically have a plurality of servicingbase stations which receive and transmit signals to users' deviceswithin the service area of the respective base stations. Communicationbetween a user and their respective base station is maintained as a usermoves about the network service area by handing off the user from onebase station to another.

Many new services are being offered to customers of wirelesscommunication carriers. One such service is providing customers withmultimedia content via the wireless communication network. For example,it is desired to provide audio/video content to customers as they moveabout the network.

Providing multimedia content via wireless communication networkspresents several challenges. For example, maintaining bi-directionalcommunication with a large group of customers that want to receive thecontent can utilize large amounts of network resources. In addition,keeping track of the customers as they move about the network and enterand leave the service areas of different base stations, and are“handed-off” to different base stations within the wireless network canconsume large amounts of network resources.

Therefore, there is a need for improved systems, apparatus, andtechniques for providing content, such as multimedia content, tocustomers via a wireless communication network.

SUMMARY

The present invention includes methods, apparatuses, and systems asdescribed in the written description and claims. In one example, contentis collected for distribution over a wireless communication network. Thecontent can include multimedia data, such as audio/video data, movies,game, audio broadcasts, television network programs, or other types ofmultimedia content. The content is accumulated and encapsulated intodata streams that are ruggedize for broadcast over a wirelesscommunication channel.

In one embodiment of a wireless broadcasting system, the content streamis encapsulated into a stream of transport packets for broadcast overthe wireless communication link. The stream of transport packets aresimultaneously broadcast as part of an identical signal from a pluralityof synchronized transmitters in a single frequency network. In otherwords, each transmitter transmits an identical signal that includes thetransport packets.

In one embodiment, a receiver is configured to receive an identicalorthogonal frequency division multiplexed (OFDM) signal from a firsttransmitter of a plurality of transmitters in a wireless broadcastnetwork. The plurality of transmitters are configured to simultaneouslytransmit the identical OFDM signal. The receiver synchronizes to theidentical OFDM signal, and receives the identical OFDM signal from asecond transmitter of the plurality of transmitters while maintainingsynchronization with the identical OFDM signal. Thus, once the receiveris synchronized to a transmitter in the network, the receiver mayreceive signals from any, or multiple, transmitters within the networkregardless of the origin of the signal.

In one embodiment, the content is encoded as digital video broadcast forhandset (DVB-H) data. This data is encoded and transmitted as an OFDMsignal in a single frequency network using techniques similar totransmission techniques developed by the Institute of Electrical andElectronics Engineers (IEEE) standard 802.16 and the WorldwideInteroperability for Microwave Access (WiMAX) forum.

Other features and advantages of the present invention should beapparent after reviewing the following detailed description andaccompanying drawings which illustrate, by way of example, aspects ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, advantages and details of the presentinvention, both as to its structure and operation, may be gleaned inpart by a study of the accompanying exemplary drawings, in which likereference numerals refer to like parts. The drawings are not necessarilyto scale, emphasis instead being placed upon illustrating the principlesof the invention.

FIG. 1 is a block diagram of a communication network for a broadcastservice network according to an exemplary embodiment of the invention.

FIG. 2 is a block diagram illustrating further detail of an examplebroadcast communication network according to an exemplary embodiment ofthe invention.

FIG. 3 is a diagram illustrating a frame structure such as can be usedin the broadcast system according to an exemplary embodiment of theinvention.

FIG. 4A is a block diagram illustrating application, data-link, andphysical layers of the broadcast system according to an exemplaryembodiment of the invention.

FIG. 4B is a diagram illustrating additional detail of one embodiment ofan IP encapsulator 412 according to an exemplary embodiment of theinvention.

FIG. 4C is a diagram illustrating an example encapsulation of oneembodiment of an IP encapsulator 412 according to an exemplaryembodiment of the invention

FIG. 5A is a diagram illustrating an example aggregate content streamaccording to an exemplary embodiment of the invention.

FIG. 5B is a diagram illustrating one embodiment of providinginformation used by a receiver to reduce power consumption according toan exemplary embodiment of the invention.

FIG. 6 is a block diagram illustrating a protocol layering model andassociated modules that perform processes in accordance with variousprotocols according to an exemplary embodiment of the invention.

FIG. 7 is a diagram illustrating mapping between bearer protocols andtheir corresponding physical layer channels according to an exemplaryembodiment of the invention.

FIG. 8 is a block diagram illustrating data flow from a convergencelayer 610 down through a MAC common part sublayer 612 according to anexemplary embodiment of the invention.

FIG. 9 is a state diagram illustrating aspects of processing accordingto the air link management protocol implemented by the air linkmanagement module 631 of FIG. 6.

FIG. 10 is a state diagram illustrating aspects of processing accordingto the initialization state of the air link management protocol of FIG.9.

FIG. 11 is a block diagram illustrating an example base stationidentification (BSID) according to an exemplary embodiment of theinvention.

FIG. 12 is a state diagram illustrating operating states for a moduleoperating in accordance with the persistent state protocol of the airlink management protocol of FIG. 9.

FIG. 13A is a state diagram illustrating aspects of processing accordingto the time slicing state protocol of the air link management protocolof FIG. 9.

FIG. 13B is a state diagram illustrating sub-states within the activetime slicing state of FIG. 13A.

FIG. 14 is a state diagram illustrating aspects of processing accordingto the scan state protocol of the air link management protocol of FIG.9.

FIG. 15 is a flow diagram illustrating aspects of the scanning processaccording to the scan state protocol of FIG. 14.

FIG. 16 is a state diagram illustrating aspects of processing accordingto the handover state protocol of the air link management protocol ofFIG. 9.

FIG. 17 is a state diagram illustrating the states of the overheadmessage module 636 of FIG. 6.

FIG. 18 is a state diagram illustrating the states of the sharedsignaling MAC module 636 of FIG. 6 at the mobile station.

FIG. 19 is a state diagram illustrating states of the downlink trafficchannel MAC protocol module 644 of FIG. 6.

FIG. 20 is a state diagram illustrating the states of the physical layercontrol protocol module 652.

FIG. 21 is a flow diagram of one exemplary embodiment of a method ofbroadcasting data according to the invention.

FIG. 22 is a flow diagram of an exemplary embodiment for receivingbroadcast data in a single frequency network having a plurality oftransmitters according to the invention.

FIG. 23 is a block diagram of an exemplary embodiment of a receiver in abroadcast system according to the invention.

FIG. 24 is a block diagram of an exemplary embodiment of a transmitterin a broadcast system according to the invention.

FIG. 25 is a flow diagram of an exemplary embodiment of a method forassigning a connection identifier to a plurality of IP content streamsin a broadcast system according to the invention.

FIG. 26 is a flow diagram of another exemplary embodiment of a methodfor assigning a connection identifier to a plurality of IP contentstreams in a broadcast system according to the invention.

FIG. 27 is a flow diagram of an exemplary embodiment of a method ofmanaging a wireless communication link in a broadcast system accordingto the invention.

FIG. 28 is a flow diagram of another exemplary embodiment of a method ofmanaging a wireless communication link in a broadcast system accordingto the invention.

FIG. 29 is a flow diagram of another exemplary embodiment of a method ofmanaging a wireless communication link in a broadcast system accordingto the invention.

DETAILED DESCRIPTION

Certain embodiments as disclosed herein provide for methods and systemsfor communication over a broadband wireless air interface. After readingthis description it will become apparent how to implement the inventionin various alternative embodiments and alternative applications.However, although various embodiments of the present invention will bedescribed herein, it is understood that these embodiments are presentedby way of example only, and not limitation. As such, this detaileddescription of various alternative embodiments should not be construedto limit the scope or breadth of the present invention as set forth inthe appended claims.

In one embodiment, the system described is a broadcast only system. Inother words, data is unidirectionally transmitted from base stations ina wireless network infrastructure to mobile stations in the network, andthere is no communication from the mobile stations back to the basestations. In the description that follows broadcast systems are alsoreferred to as data-casting systems. Because the base stations arebroadcast only, there is no limitation on the number of mobile stationsreceiving the base stations' signal. Also, because there is nocommunication from the mobile stations back to the base stations, thebase stations do not need to communicate to each other to monitor when amobile station is going to leave one base station's coverage area andenter another base station's coverage area.

In one embodiment, multiple base stations in a single frequency network(SFN) covering a particular geographic region are synchronized andtransmit an identical signal at the same time. Because all of the basestations in a single frequency network transmit the same signal and aresynchronized, mobile stations within the single frequency networkreceive the same signal from any base station, or multiple basestations, within the single frequency network and thereby provide a formof macro-diversity. As a mobile station moves about the SFN and leavesthe coverage area of one base station and enters the coverage area ofanother base station, there is no “handoff” the mobile station simplybegins receiving the same signal that originated from a different basestation. In addition, the mobile station can combine signals it receivesthat originated from multiple base stations, thereby benefiting frommacro-diversity.

All of the base stations within a single frequency networksimultaneously transmit the same signal or waveform. In certain types ofknown wireless communication networks, data is transmitted in “frames”that can use different modulation schemes and different coding rates fordata contained within each frame. In addition, frames transmitted by onebase station in such a known network will be different than framestransmitted by other base stations in the network, because each basestation transmits different data and can be using different modulationschemes and coding rates. Also, in these known networks, differentmodulation schemes and coding rates can be used, for example, to providedifferent quality of service (QoS) to different users, and themodulation and coding rates can be changed from frame to frame inresponse to the changing requirements of users of the communicationnetwork. In contrast to such known networks, in the exemplary broadcastsystem of the present invention described above, all of the basestations in a single frequency network transmit the same datasynchronously, with the same modulation scheme and the same coding rate,resulting in the same signal being broadcast from all base stations. Inthis way, a mobile station can receive transmissions from any of thebase stations in the single frequency network and combine them toimprove operation of the mobile station as it moves about within thenetwork.

The unidirectional broadcast system described herein offers advantagesover conventional two-way communication systems, such as two-way systemsbased on the IEEE 802.16 standard, for delivering content to multiplereceiving devices simultaneously. One such advantage is that thebroadcast system of the present invention may be able to make use ofcertain portions of the RF spectrum that are inefficient forconventional two-way communication systems. For example, the RF spectrumhas been divided into various portions that are allocated for differentuses, and there are regulations about the level of RF emissions a devicemay radiate into adjacent portions of the spectrum. Various techniqueshave been developed to comply with these regulations. One technique isto filter the RF transmission by a device, but filtering can requireadditional components that increase the size and power consumption ofdevices. Increased size and power consumption may make it impractical toinstall sufficient filtering in a mobile device. In the broadcast systemof the present invention, the base stations that transmit the broadcastsignal can support the filter size and power consumption, and becausethe mobile devices do not transmit up to the base stations in thisbroadcast system, they do not require any transmit filtering. In thisway, portions of the spectrum that may be practically unusable, ordifficult to use, for two-way communication systems can be efficientlyused for the unidirectional broadcast system of the present invention.

In one embodiment, content is encoded as digital video broadcast forhandheld (DVB-H) data. This data is encoded and transmitted as an OFDMsignal in a single frequency network using techniques similar totechniques developed by the Institute of Electrical and ElectronicsEngineers (IEEE) standard 802.16 and the Worldwide Interoperability forMicrowave Access (WiMAX) forum. For example, a DVB-H MAC layer output,such as a Multiprotocol Encapsulated (MPE) MPEG-2 TS can by input toWiMAX MAC and PHY layer using OFDM to broadcast Orthogonal FrequencyDivision Multiplexed (OFDMA) or Orthogonal Frequency Division MultipleAccess (OFDMA), jointly referred to as OFDM. FIG. 1 is a block diagramof a communication network for a broadcast service network, according toone embodiment of the invention. As shown in FIG. 1, the networkincludes a mobile station (MS) 106 and an access service network 110. InFIG. 1, only one MS 106 is shown, but there would typically be many MSs106. In the following description the receiving station is referred toas a mobile station, but the receiving station may be mobile or it maybe stationary.

The access network 110 includes a broadcast management module 111 and anencapsulator 116. The encapsulator 116 can encapsulate many differentdata protocols, for example, in one embodiment the encapsulator can bean IP encapsulator. The broadcast management module 111 includes atleast one base station transceiver (BTS), or base station (BS), 112 aand 112 b, and a single frequency network adapter 114. The accessnetwork 110 also includes an IP encapsulator 116. In the example of FIG.1, two BSs 112 a and 112 b are shown, but any desired number of BSs maybe included within the access network 110. The BS's within the accessnetwork 110 transmit using a same frequency band and thereby renderaccess network 110 a single frequency network (SFN). In communicationwith the access service network 110 is at least one content provider 120a. Typically there would be a plurality of content providers 120 a-120 nin communication with the access service network 110.

The content providers 120 a-120 n provide content to the access servicenetwork 110. The content may include, for example, a digital form ofaudio, video, graphics, multimedia, movies, or other forms of content.Content from the content providers 12 a-120 n is received by the IPencapsulator 116 in the access service network 110. The IP encapsulator116 collects the content, or data, and ruggedize the data fortransmission over a wireless communication link. The IP encapsulator 116may, for example, perform channel coding and time slicing of thecontent. The IP encapsulator 116 may also add information about thecontent to the data. The IP encapsulator 116 then provides theruggedized data to the single frequency network adapter 114 fordistribution to the various base stations.

The single frequency network adapter 114 receives the ruggedized datafrom the IP encapsulator 116 and schedules it for broadcast over the airby the BSs 112 within access network 110. Scheduling of the data forbroadcast from multiple BSs 112 a and 112 b includes synchronizing thebroadcasts from the multiple BSs 112. As explained further below,multiple BS 112 a and 112 b transmit the same data at the same time sothat a MS 106 can receive the same signal from multiple BSs 112 a and112 b.

Data from the single frequency network adapter 114 is communicated tothe BS's 112 a and 112 b for broadcast over the air. The BSs 112 a and112 b may broadcast signals into the coverage area of the base stationthat has been divided into one or more sectors. For example, in theexample of FIG. 1, a first BS 112 a includes a broadcast coverage areathat is divided into three sectors 122, 124, and 126. Use of sectors canprovide improved performance over a non-sectorized BS, includingmultipath diversity within areas of overlapping sectors, as well asbroadcasting more energy into individual sectors that a correspondingomni-directional antenna.

In one embodiment, there is no direct interface or communication betweenthe BS's 112 a and 112 b within the access service network 110. Asdescribed further below, because all of the base stations transmit thesame signals at the same time, there is no need for the BS's to haveknowledge of which MS 106 are within their respective coverage area. Inother words, because the BSs are broadcast only, and they transmit thesame signal at the same time, a MS 106 can receive signals from any ofthe BS without differentiating which BS the signal originated from. Inaddition, the MS 106 can receive signals from multiple, different BSsand combine those signals as multiple instances of the same signal.

FIG. 2 is a block diagram illustrating further detail of an examplebroadcast communication network. Content providers 202 distributecontent to a content processing module 204. The content distributed bythe content providers can be various digital forms of audio, video,multimedia, and other forms of content. The content can be, for example,audio/video streams, motion picture expert group-2 (MPEG-2), MPEG-4,windows media video (WMV), stored data files, meta-data, and otherformats. The content processing module 204 receives the various content,processes it, and outputs streaming media for each content using, forexample, real time streaming protocol, real-time protocol, InternetProtocol (RTSP/RTP/IP).

In one embodiment, the media from the content processing module 206 iscommunicated to an encoder/transcoder module 206 that encodes the mediainto an encoding-standard compatible stream, such as the H.264 encodingstandard. For example, the media content can be encoded using H.264,also known as MPEG-4, Part 10. The encoded rate for the combined audioand video may be approximately 300 to 400 kb/s. In another embodiment,content can be provided by other sources 295. For example, in oneembodiment “raw” media content, such as raw audio/video data iscommunicated to the encoder/transcoder 206. In this embodiment, theencoder/transcoder 206 acts as a source encoder to encode the media. Instill another embodiment, media previously encoded can be communicatedto the encoder/transcoder 206 where the media is transcoded into adesired format. For example, media that has already been encoded intoone format can be received from a content source 205 and transcoded intoa desired different encoding format.

The encoded media can be, for example, further encapsulated using theReal-Time Protocol (RTP), the User Datagram Protocol (UDP), and theInternet Protocol (IP). The payload of the encoder module 206 iscommunicated to a server 208 where it is transmitted as an RTP/UDP/IPstream. The RTP/UDP/IP stream is communicated to an IP encryption module210 that encrypts the stream and communicates it to an IP multicastintra/inter network 220. The IP multicast intra/inter network 220 alsoreceives electronic service guide (ESG) information about the variouscontent from an ESG server 222. The IP multicast intra/inter network 220can be a private network, or a virtual private network, or a publicnetwork such as the Internet. In this regard, the IP encryption module210 can optionally be provided at another location in the system, suchas at or just after encoder 206, or at or just before IP Encapsulators230 and 232, depending on the security level of IP multicast intra/internetwork 220, among other factors.

Encrypted content and ESG data is streamed via the IP multicastintra/inter network 220 to IP encapsulator modules 230 and 232. In theexample of FIG. 2, two IP encapsulators 230 and 232 are illustrated, butin other embodiments of the broadcast system there could be more thantwo IP encapsulators in which each IP encapsulator serves a single SFN,or there could be a single IP encapsulator which serves multiple SFNs.Each IP encapsulator is included within a single frequency network,e.g., 240 and 242.

The IP encapsulators 230 and 232 receive the IP stream from the IPmulticast intra/inter network 220 at a network interface 234, 236. Asdescribed further below, the IP encapsulators 230 and 232 process the IPstreams and output IP/MAC (Media Access Control) streams at a modulatorinterface 235, 237. The IP/MAC streams are communicated to SFN adaptermodules 250 and 252 each of which distributes the IP/MAC streams to oneor more BS's in a synchronized manner. The output of the SFN adapters250 and 252 are communicated to a plurality of BS's, 260 and 262 withineach respective SFN. Accordingly, an MS 270 can move about within acoverage area of a SFN 240 and receive broadcast signals from any, ormultiple, BS's 260 within the SFN. An SFN is a collection of basestations, all operating at the same modulation scheme and coding rate,and all transmitting the same signal synchronously on a same frequencyband.

Returning now to the IP encapsulator modules 230 and 232, as describedfurther below, an IP encapsulator receives a finely interleaved IPstream from the multicast intra/inter network 220 on its networkinterface 234 and 236 and produces coarsely interleaved IP/MAC streamson its modulator interface 235 and 237. In one embodiment, an IP/MACstream is a stream of MPEG-2 Transport Stream (TS) packets, that havebeen further encapsulated using Multi-Protocol Encapsulation withForward Error Correction (MPE-FEC). The encapsulation process usingMPE-FEC places IP packets into an interleaving array indexed by the IPsource/destination address information (i.e. multiple IP streamsarriving from the IP network are demultiplexed into buffers, with thesebuffers serving as interleaving arrays). In one embodiment, the IPencapsulator will compute a Reed-Solomon parity sequence on the IPpackets placed in the interleaving array. Both the IP packets and theReed-Solomon parity information are encapsulated into MPEG-2 sections.These sections may be further fragmented and encapsulated into MPEG-2transport streams (TS) of packets. Of course, it can be appreciated thatother forms and protocols of encoding, encapsulation and interleavingcan be used to form the streams without departing from the scope of theinvention.

In one embodiment, the content streams can be coarsely interleaved toallow for a power savings mechanism at the MS, referred to astime-slicing that is described in further detail below. In anembodiment, finely interleaved content, for example IP encoded content,is received and buffered, and then the buffered content is rearrangedinto coarsely interleaved content. For example, buffering at the IPencapsulator enables seconds worth of IP packets corresponding to aparticular content (“program”) to be received in a continuous, or nearlycontinuous, stream via the network interface. This buffered data canthen be encapsulated and channel coded using MPE-FEC and sent all atonce, creating a coarsely interleaved IP/MAC stream. Using thistechnique, the TS packets emerging from the modulator interface of theIP encapsulator are coarsely interleaved, with one “program” being theonly packets sent for hundreds of milliseconds, followed by a lengthyset of packets for another program. A program can be considered, forexample, a collection of IP/MAC streams that are meant to be renderedjointly at the MS (e.g. a television program's audio, video, andteletext) to deliver a particular content. This coarse interleavingallows a mobile station's receiver to power on and receive desiredpackets for a particular program, and then reduce power by not receivingthe packets that are transmitted which belong to programs which are notwanted by that mobile station. This time slicing functionality canresult in a significant power savings at the mobile station.

As mentioned above, the IP/MAC streams are forwarded by the IPEncapsulators 230 and 232, via SFN Adapters 250 and 252, to a modulatorat each of the base stations 260 and 262 that make up the singlefrequency networks. Within each SFN, all of the BS modulators are timesynchronized. So, when the IP/MAC streams are received at the modulatorswithin a given SFN, the fact that the information to be transmitted isidentical, coupled with the modulators being time synchronized, causesthe signals emitted from all modulators in the SFN to be the same, ornearly the same.

At the MS, the IP/MAC streams must be received by the mobile station'sapplication layer and interpreted. The application in the MS willinterpret service information (SI) that is included in the IP/MACstreams and, along with the electronic service guide (ESG), willdetermine what content is available in the aggregate IP/MAC stream. Thiswill be presented to the user in the form of an electronic program guide(EPG). This allows the user to select which IP/MAC streams he desires,subsequently allowing his receiver to capture, demodulate and forwardonly the selected content up to the application layer.

FIG. 3 is a diagram illustrating a frame structure such as can be usedin the broadcast system according to one embodiment of the presentinvention. As illustrated in FIG. 3, the frame 302 structure is dividedinto multiple sub-channels 304 (the vertical axis in FIG. 3), with eachsub-channel using a carrier frequency that is orthogonal to carrierfrequencies of other sub-channels. The frame 302 is also divided in timeinto symbol periods 306 (the horizontal axis in FIG. 3). As illustratedin FIG. 3, in a frame 302, data may be carried on each of thesub-channel carrier frequencies 304 simultaneously during individualsymbol periods 306. The frame scheme illustrated in FIG. 3 is commonlyused in wireless communication systems based on OFDM.

In the present system, the OFDM frame 302 can be optimized for atransmit only system. As shown in FIG. 3, the frame includes a preambleduring symbol period 0. During symbol periods 1 and 2, the frame 302includes a frame control header (FCH) 310 and a downlink map (MAP) 312.Generally, the FCH 310 includes information about the frame 302configuration, such as coding schemes, message lengths, usablesub-channels, and the like. The MAP includes information about thelocation of downlink content with the OFDM frame 302. The remainingsymbol periods 314, symbol periods 3 to N, will carry the informationreceived in the IP/MAC streams from the IP encapsulator module 230 ofFIG. 2. In one embodiment, optimization of the frame 302 can beimplemented, for example, at the base station 112 of FIG. 1, or at thesingle frequency network adapter 250 of FIG. 2. In other embodiments,the optimization can be implemented in other portions of the broadcastsystem.

It is noted that there is no uplink map provided in the OFDM frame 302.This is because, being a unidirectional broadcast only service, the MS'sdo not transmit back to the BS's in the SFN. Thus, after the OFDM frame302 has been transmitted, a second OFDM frame 320, formatted in asimilar manner as OFDM frame 302, is transmitted.

FIG. 4A is a block diagram illustrating application, data-link, andphysical layers of the broadcast system. As shown in FIG. 4A, the layerson the left are implemented on the transmit side 402 of the airinterface and the layers on the right are implemented on the receiverside 404 of the air interface in the broadcast system. In oneembodiment, the top two layers 410 and 412 on the left can beimplemented by modules for a common SFN, or other modules within thebroadcast infrastructure, and the bottom layer 414 can be implemented byeach base station in the SFN as shown in FIG. 2. In one embodiment, allof the layers on the right can be implemented by the mobile station 106of FIG. 1, or the mobile station 270 of FIG. 2. In other embodiments, itis possible that the receiver layer 420 can be implemented in the MS,and the application layer 424 and data link layer 422 can be implementedin a device to which the MS is connected.

Returning to FIG. 4A, at the transmit side 402, an encoder module 410provides IP packets of content to an IP encapsulator module 412. The IPencapsulator 412 is located at the top of a data link layer,encapsulating IP packets with an outer channel code and with timeinterleaving information and then communicating the resultant MPEG-2transport stream (TS) packets to a transmitter module 414 located in abase station. An air interface protocol governs the operation oftransmitter module 414 and receiver module 420. Data transmitted fromthe transmitter 414 to the receiver 420 via an air interface can beincluded in one or more frames, such as the frame described in FIG. 3.

At the receive side 404, the receiver module 420 outputs the datareceived as MPEG-2 TS packets. An upper data link layer (MPE-FECreceiver) module 422 receives the MPEG-2 TS packets and outputs IPpackets to an application decoder module 424. In the upper data linklayer (MPE-FEC receiver) module 422, a multiprotocol encapsulation withforward error correction (MPE-FEC) receiver module extracts timeinterleaving information and provides input based upon this informationto the receiver module 420 to accomplish power savings in the receiver.Aspects of the time interleaving and feed back power savingsinformation, referred to as “time slicing” are described further below.

In the broadcast system, a mobile station on receive side 404 typicallyperforms many functions, for example, it searches for and selects anetwork, receives and de-capsulates PDUs, scans for and performshandover to adjacent broadcast networks (SFNs) if required, and consumesMAC management messages produced by a base station 402.

The mobile station on receive side 404 includes an air link managementmodule that operates in accordance with an air link management protocol(ALMP) to manage the state of the mobile station as it relates tobroadcast network attachment. In a typical operation, when a mobilestation 404 is powered on, it searches for and selects a suitablebroadcast network, also referred to as an IP data-casting network. Thismay be accomplished by first searching for a predetermined preamblewaveform on a set of predetermined orthogonal frequencies. Thesepredetermined frequencies can be based upon a list of possiblefrequencies, as well as on a cache of previously used frequencies. Oncea suitable preamble waveform is detected, the information containedwithin a downlink DL-MAP (item 312 in FIG. 3) may be captured and usedto determine if the network is a broadcasting network, or another typeof network, such as a two-way communication system that is also inaccordance with the IEEE 802.16 standard. If it is determined that thenetwork is not suitable, it may be possible to use information about thenetwork to improve, or speed up, the frequency searching process. Once asuitable, or preferred, broadcast network is found, the mobile stationcan synchronize its receiver module to the network and begin receivingMAC data bearing PDUs. If no suitable broadcast network is found, themobile device can enter into a power conservation mode, similar to anout-of-service-area mode in traditional cellular handset systems.

Once a mobile station on receive side 404 has synchronized its receiverto the broadcast signal, the upper layers 422 and 424 on receive side404 can synchronize to the arriving MPEG-2 TS packet stream. This may bedone using the service information included in the MPEG-2 stream.

Once the application layer 424 on receive side 404 has synchronized tothe arriving IP/MAC streams, it can select one or more streams toreceive and in so doing, it can direct the receiver to turn “off” duringslices of time when the desired packets are not being transmitted. Thispower savings technique is referred to as time slicing, and is describedfurther below. When a mobile station is time slicing, it will interpretthe arriving IP stream and extract from the headers encapsulating the IPpackets, information necessary to accomplish time slicing. Thisinformation informs the receiver when the current time slice of thedesired content will end and when the next time slice of the desiredcontent will begin. Knowing the beginning and end of the desired timeslices allows the mobile station to keep its receiver 420 “on” until thecurrent desired time slice completes and then to power down the receiver420 until the next desired time slice begins.

FIG. 4B is a diagram illustrating additional detail of one embodiment ofan IP encapsulator 412 according to an exemplary embodiment of theinvention. As shown in FIG. 4B, the IP encapsulator 412 includes aninterleaving and forward error correction (FEC) module 440. Theinterleaving and FEC module 440 receives finely interleaved IP packets,then coarsely interleaves the IP packets, adds forward error correctioninformation, and outputs content sections to a transport streamencapsulator module 442. The transport stream encapsulator module 442encapsulates the sections into transport stream (TS) packets.

The IP encapsulator 412 also includes a table segmentor module 444 thatreceives program specific information and service information andformats the information into sections. The program specific informationcan include a program guide that includes information that identifiesthe beginning of an event, for example, when a specific program willbegin. Another example of program information is a list of the differentcontent that is available. For example, if the content is being streamedreal-time, the information can include a list of the different contentstreams that are currently available. A transport stream encapsulatormodule 446 receives the sections from the table segmentor module 44 andencapsulates the sections into transport stream (TS) packets. Atransport stream multiplexor module 448 receives the outputs of the twotransport stream encapsulators 442 and 446 and outputs an aggregatetransport stream.

FIG. 4C is a diagram illustrating an example encapsulation of oneembodiment of an IP encapsulator 412 according to the invention. In theexample of FIG. 4C, an IP packet 460 is received and wrapped with asection header and trailer to form a multi-protocol encapsulated—forwarderror corrected (MPE-FEC) section 462. In one embodiment, the IP packet460 shown in FIG. 4C contains H.264 encoded data and has IP, UDP and RTPprotocol headers. The MPE-FEC section 462 is then partitioned intotransport stream packets 464. In one embodiment, the transport streampackets 464 are MPEG-2 TS packets.

FIG. 5A is a diagram illustrating an example aggregate content streamrepresented by the MPEG-2 TS packets shown in FIG. 4. As shown in FIG.5A, content from various sources 504, 506, and 508, are combined into anaggregate content stream 502. The content 504, 506, and 508 is coarselyinterleaved (as discussed above) into the aggregate stream 502, wherethe content is grouped into a “burst” of data for one content stream,followed by a “burst” of data for each of the other content streams. Forexample, the aggregate stream 502 includes a first content stream 504 a,followed by a second content stream 506 a, a third content stream 508 a,and so on until a desired number of content streams have beenaggregated. Then, the next chronological portions for the contentstreams are transmitted. For example, the next portions of the firstcontent stream 504 b, the second content stream 506 b, and the thirdcontent stream 508 b are transmitted. In one embodiment, the aggregationof the content streams can be implemented by the IP encapsulator module116 of FIG. 1, or by the IP encapsulator 230 of FIG. 2. In otherembodiments, the aggregation is implemented in other modules within thesystem.

In one embodiment, a single connection identification descriptor isassigned to the aggregate content stream. For example, a singleconnection identification descriptor can be used for all of theindividual content streams contained in the aggregate content stream. Inanother embodiment, a unique connection identifier is assigned to eachrespective content stream contained in the aggregate stream 502.

When a mobile station desires to receive one, or more, of the contentstreams in the aggregate stream 502, a burst of the desired contentstream is followed by a time period of other, non-desired contentstreams. A mobile station may improve power savings by using a timeslicing technique where portions of the mobile station that receive andchannel decode the aggregate stream, referred to as the receiver, can bepowered on to capture the desired content streams and then powered downduring the non-desired content streams. In one embodiment, programinformation about the content in the aggregate content stream isincluded within the aggregate stream. The program information caninclude a program guide with information identifying, for example, whena particular program is going to begin, its duration, etc. In addition,the program information can identify programs that are currentlyavailable, such as, if the content is being streamed real-time.

A filtered stream 510 in FIG. 5A illustrates aspects of time slicing. Inone embodiment, a device receiving the content can use programinformation to identify when desired content is going to be availableand deactivate a receiver until the desired content is available. Inanother embodiment, the device can use program information to identifywhat content is currently available and use that information to acquiredesired content from the content being received. Once a receiving devicehas identified desired content and has synchronized to the content,additional information in the content stream can be used to activate anddeactivate a receiver at desired times to acquire the content at itsrecurring time slices while conserving power. In the example of FIG. 5A,the first content stream 504 of the aggregate stream 502 is desired. Asillustrated in FIG. 5A, the mobile station powers on its receiver duringa time 512 corresponding to the first portion of the first contentstream 504 a. The mobile station can then power down the receiver duringthe period of time 514 after the end time of 504 a and before the starttime of the second portion of the first content stream 504 b, therebyavoiding having to receive undesired content between the slices ofdesired content. During the period of time 516, when the second portionof the first content stream 504 b is received, the mobile station powerson the receiver. This process continues until either the desired contentstream terminates, or a user selects a different content stream as thedesired content stream.

In one embodiment, information about the duration of time 512corresponding to the first portion of the content stream, and theduration of time 514 before the start of the next segment of the desiredcontent 516 can be communicated to the device receiving the content.Similar information for the other portions of the content stream canalso communicated to the receiving device. In this way a devicereceiving the content can use the information to turn on and offportions of the receiver at the appropriate times to thereby reducepower consumption.

FIG. 5B is a diagram illustrating one embodiment of providinginformation used by a receiver to reduce power consumption according toan exemplary embodiment of the invention. As shown in FIG. 5B, a firstburst 550 of desired content is followed by a second burst 552 of thedesired content later in time. In the example illustrated in FIG. 5B,the burst of desired content is made up of sections. For example, thefirst burst 550 of desired content is made up of four sections 560, 562,564, and 566. Likewise, the second burst 552 of desired content is alsomade up of four sections 570, 572, 574, and 576. Information can beincluded in the sections that can identify when the current burst willend and also can include information about when the next burst ofcontent will begin. In one embodiment, information included within thefour sections 560, 562, 564, and 566 of the first burst 550 of desiredcontent include information indicating the end time of the first burst550 and a value indicating the time 580 from the start time of the firstburst 550 to the start time of the second burst 552. Similar informationcan be included within the four sections 570, 572, 574, and 576 of thesecond burst 552 of desired content about a subsequent burst of desiredcontent that will follow the second burst 552. Other embodiments caninclude different numbers of sections in a burst, as well as differentinformation about the occurrence of a subsequent burst of desiredcontent.

In one embodiment, the aggregate stream 502 is transmitted by multipleOFDM frames and each frame includes the same connection identifiervalue. In this way all of the devices receiving the aggregate contentstream 502 use the common connection identifier to identify theconnection and then use information about the times that desired contentis present in the aggregate content stream 502 to turn their receiverson and off at appropriate times. In another embodiment, the OFDM framesdo not include a connection identifier.

Returning to FIG. 5A, in another embodiment, the aggregate contentstream 502 is transmitted as multiple OFDM frames and each frameincludes a connection identifier that identifies the content in theframe. In other words, frames that include the first content stream 504would have one connection identifier and frames that include contentfrom a second content stream 506 would have a second connectionidentifier, and so on. A frame could also include data from multiplecontent streams, and the frame would include one or more connectionidentifiers that reflect the content of the frame. In this embodiment,all devices receiving the aggregate content stream 502 would power onduring the beginning of each frame and determine if the frame includesdesired content. If it does, then the device would remain on to receivethe content, if not the device would power down until the beginning ofthe next frame when it would power up to determine if the frame includesdesired content.

During the time period 514 between the reception of portions of thedesired content stream, or between the beginning of OFDM frames that donot include desired content, the mobile station can use its receiver toperform other functions. For example, the mobile station can scan foradjacent broadcast networks. Information enabling the mobile station tosearch for adjacent broadcast networks can be programmed into the mobiledevice at manufacture time and/or it can be announced by the networkusing system delivery descriptors, such as elements of the MPEG-2service information. The mobile station can scan these adjacentnetworks, and if a broadcast signal is found, it can be noted for futureuse. If the current broadcast network is lost or degrades to anunacceptable level, the mobile station can first search the “foundnetworks” identified during the scanning process for a replacementbroadcast signal before engaging in a full frequency scan for anotherbroadcast network.

Overview of Broadcast Layering Model

FIG. 6 is a diagram illustrating a layering model and associated modulesthat perform processes in accordance with various protocols to implementan example embodiment of the present invention. One or more instances ofeach protocol exist on each side, transmit and receive, of the wirelessair interface link. These protocols are grouped into two distinct types:bearer protocols 602 and non-bearer protocols 604. A given layer isgenerally composed entirely of modules that support either bearerprotocols 602 or non-bearer protocols 604. A bearer protocol is aprotocol that is involved with the transmission/reception of content(payload) data across the air interface, and a non-bearer protocol is aprotocol that is involved with the transmission/reception of controlmessages across the air interface. The layers are also referred to asbearer and non-bearer layers, depending on the types of modules andprotocols associated with the respective layer. Bearer and non-bearerprotocols can be implemented by various modules on both the receive sideand the transmit side, of the broadcast system. In one embodiment,protocols implemented on the receive side are implemented by modules inthe mobile station, such as the mobile station 106 of FIG. 1 or themobile station 270 of FIG. 2, and protocols implemented on the transmitside are all implemented by modules in a base station, such as basestations 260 of FIG. 2.

As mentioned above, modules that include bearer protocols are involvedwith the transfer of content (payload) data over the wireless link.Bearer protocols are typically called in a specific order, which canform both a transmit chain and a receive chain. On the transmit side, amodule that is processing in accordance with an associated protocolaccepts a Service Data Unit (SDU) as input, and produces one or moreProtocol Data Units (PDUs) as output. A module transforming an SDU intoPDUs may perform several functions. For example, the module processingin accordance with the protocol may perform a transformation on the SDU,such as encryption. The protocol may also add a header, or a trailer tothe SDU. In addition, the protocol may combine multiple SDUs into asingle PDU, a process referred to as “packing,” or split an SDU intomultiple PDUs, a process referred to as “fragmentation.”

On the receive side, modules processing in accordance with associatedprotocols accept a PDU as input, and produce an SDU as output. Intransforming the PDU into a SDU, the module may perform severalfunctions. For example the module processing in accordance with theprotocol may perform a transformation on the remaining PDU, such asdecryption. The protocol may also remove a header or a tail from thePDU. In addition, the protocol may extract multiple SDUs from a singlePDU, a process referred to as “unpacking,” or de-multiplex multiple PDUsto form a single SDU, a process referred to as “reassembly.”

Referring again to FIG. 6, a session control sublayer module 606includes non-bearer protocols, and so does not carry payloads on behalfof other “bearer” protocols. The session control sublayer 606 isgenerally responsible for system configuration and state maintenance.Because the system described herein is a broadcast system, there istypically no concept of a mutual state held at both the mobile stationand the base station. In one embodiment processes and protocols definedin the session control sublayer module 606 can be used for configurationand provisioning information to be disseminated to other layers, or froma base station to mobile stations.

Corresponding to the non-bearer protocol session control sublayer module606 is a bearer protocol upper MAC sublayer module 608. The bearerprotocol upper MAC sublayer module 608 includes a convergence sublayermodule 610 that provides a conduit for upper protocols/applications totransport their data over a MAC layer defined in an air interface. Theconvergence sublayer 610 generally supports the protocols, interfaces,encapsulations and mappings to accommodate the needs of the upperlayers.

The bearer protocol upper MAC sublayer module 608 also includes a MACcommon part sublayer module 612. Included within the MAC common partsublayer 612 is a scheduler module 614 and an xDU transformation module616. In the broadcast service of the present invention, the schedulermodule 614 exists only on the transmitter, or base station. Thescheduler module 614, operating in accordance with a scheduler protocol,arbitrates access to the downlink data channel (DCH) for two differenttypes of bearer protocols, signaling messages and MPEG-2 transportstream. The xDU Transformation module 616, operating in accordance withan xDU transformation protocol, encapsulates SDUs it receives from theconvergence sublayer 610 and forms PDUs that are specifically sized tofit predetermined physical (PHY) layer containers, such as allocationregions or Hybrid Automatic Repeat reQuest (HARQ) packets. The xDUtransformation module 616 passes a frame's-worth of PDUs and a list ofPHY containers, to a security sublayer module 618. There is acorresponding module on the mobile station. In the mobile station thexDU transformation module, in accordance with an xDU transformationprotocol, re-forms SDUs from a set of PDUs and delivers the SDU to theconvergence sublayer.

A Security Control Sublayer module 620 includes non-bearer protocolsthat provide a key exchange capability for the Security Sublayer module618. Because the security control sublayer 620 is a non-bearer layer,its processing in accordance with associated protocols do not carry dataon behalf of other protocols. The security sublayer 618 operates inaccordance with bearer protocols that provide encryption/decryptioncapabilities. Because the security sublayer 618 includes bearerprotocols, it carries data on behalf of other protocols, in particularthe MAC common part sublayer.

Continuing through the layers, there is a MAC control sublayer module630. The MAC control sublayer 630 provides the ability to acquire thebroadcast system, and establish an air link. The MAC control sublayer630 includes non-bearer protocols, and so does not carry data on behalfof other protocols.

The MAC control sublayer 630 includes an air link management module 631that operates in accordance with an air link management protocol. Theair link management protocol manages the overall state machine whichdetermines the state of the air link. The air link management protocoluses other protocols, described below, to manage the functionality ofeach state. This protocol is mostly relevant to control of the mobilestation regarding initialization, acquisition, time sliced powermanagement, scanning for neighbor Single Frequency Networks (SFNs), andseamless handover between SFNs. The air link management moduleprocessing, and its related protocol modules, are described in furtherdetail below.

In support of the air link management module 631, the MAC controlsublayer 630 also includes an initialization state module 632, apersistent state protocol module 633, a time sliced protocol module 634,a scan state protocol module 635 and a handover protocol module 637. Theinitialization state module 632 operates in accordance with aninitialization state protocol to manage system acquisition andselection. It is primarily relevant to the mobile stations and enablesthe mobile stations to find a broadcast system, and to select one forwhich its subscriptions are valid. Also included in the MAC controlsublayer 630 is a persistent state module 633. The persistent satemodule 633 operates in accordance with a persistent state protocol, suchthat after synchronizing to a broadcast signal, but before allowing auser to view an actual broadcast, or datacast, a mobile station willengage the Persistent State module 633. When this module is active, thereceiver is passing the aggregate stream to the upper layers and theupper Data-link Layer, Network Layer, and Application Layer aresynchronizing to the incoming DVB-H MPEG-2 stream. This represents asecond stage of synchronization for the mobile station (the first beingsynchronization to the broadcast signal at the waveform and framelevel). Once these upper layers are synchronized, then the mobilestation can enter into the time slicing protocol, which allows forbattery savings.

Additional modules are also included in the MAC control sublayer module630. A time slicing module 634 operates in accordance with a timeslicing protocol that is primarily in effect when a mobile station isreceiving broadcast data. In accordance with the selected content, orelementary, streams in the downlink, the mobile station will cycle powerof some on-board subsystems to conserve battery life. A Scan Statemodule 635, operating in accordance with a scan state protocol, governshow a mobile station scans for alternate broadcast networks. It isactivated either when a broadcast signal is lost or during ‘off’ statesgoverned by the Time Slicing Protocol 634. Base stations broadcastsinformation about neighbor SFNs so the mobile station can optimize itsscan list and conserve battery life while scanning. Another module isthe overhead message module 636. This module operates in accordance withan overhead message protocol and receives overhead messages, andpublishes the extracted information as Public Data for access by otherprotocols. Still another module is the handover module 637. The handovermodule 637 operates in accordance with a handover protocol and managesthe handover process in the event the signal from the current SFN islost or degrading. In addition, this module can manage seamlesshandover, acting on signal quality and broadcast information aboutneighbor SFNs.

Corresponding to the MAC control sublayer module 630 and its non-bearerprotocols, there is a MAC sublayer module 640 that includes bearerprotocols. The MAC sublayer 640 includes modules that operate inaccordance with bearer protocols for processing MAC PDUs for use withthe physical layer. Because it contains bearer protocols, it does carrydata for other protocols.

Included within the MAC sublayer 640 is a shared signaling MAC module642 that operates in accordance with a shared signaling MAC protocol.This protocol transmits, at a base station, or receives, at a mobilestation, shared signaling control PDUs. At the base station, the SharedSignaling module 642 maps shared signaling control PDUs to the downlinkMAP channel (MCH) physical layer channel. The control PDUs mapped tothis channel is the compressed MAP. At the mobile station, the controlPDUs are received by the Shared Signaling module 642 and used by theDownlink Traffic MAC module 644 that operates in accordance with adownlink traffic MAC protocol. The Downlink Traffic Channel MAC protocolplaces and extracts MAC PDUs to and from the DCH physical layer channel.All MAC PDUs, whether they are MAC management PDUs or PDUs from anapplication, flow through this protocol.

Below the MAC control sublayer 630 and the MAC sublayer 640 are aphysical control layer module 650 and a physical layer module 660respectively. The physical layer control layer 650 includes a physicallayer control module 652 that operates in accordance with a physicallayer control protocol. The physical layer control module 652 handlesphysical layer (PHY) activation, and notifies other protocols ofsynchronization loss.

The physical layer 660 provides physical layer transport for air linkmessages. It consists of bearer protocols, and so carries data on behalfof their protocols. Included in the physical layer 660 is a physicallayer module 662 that operates in accordance with a physical layerprotocol. This protocol describes the basics of the OFDM physical andincludes messaging used by the physical layer, and a generalintroduction into frame structure and timing, as well as OFDM. Thisprotocol defines the details of how data is sent over the physicallayer, including coding, subchannel assignment, modulation, etc.

FIG. 7 is a diagram illustrating mapping between bearer protocols andthe physical layer channel. A physical layer channel is a region orregions in time and frequency, of the data frame 302 in FIG. 3, wherecertain MAC PDUs are transmitted with PHY parameters dictated by theparticular physical layer channel. For example, the physical layerprotocol 662 maps a frame control header channel (FCH) 702. A channel isa physical layer channel that occurs at the start of a time divisionduplex TDD frame which carries two instances of the Downlink FramePrefix (DLFP) PDU. The DLFP PDU maps to the FCH in a particular mannerthat remains unchanged from frame to frame.

There are three physical layer channels present in one embodiment of anair interface. In this embodiment, the physical layer channels include aDownlink FCH Channel (FCH) 702, a Downlink MAP Channel (MCH) 704, and aDownlink Data Channel (DCH) 706. The physical layer protocol 662 maps tothe FCH channel 702. The shared signaling MAC protocol maps to the MCH704, and the downlink data channel MAC protocol 644 maps to the DCH 706.The MCH 704 carries the downlink MAP PDU from the base station to themobile station. The DCH carries MAC PDUs from the base station to themobile station.

Returning to FIG. 6, the MAC control sublayer 630 includes an air linkmanagement module. The air link management module 631, operating inaccordance with an air link management protocol, is responsible for thegeneral state machine implementation for the MAC Control Sublayer 630.The functionality of each of the different states is implemented in aprotocol defined for that state. The air link management protocolmanages transitions between states by activating and deactivating thestate implementation protocols. There is pseudo air link managementmodule at the base station but it does not keep state.

MAC Common Part Sublayer

Following is further detail of the MAC common part sublayer module, item608 in FIG. 6. The MAC common part sublayer 608 is responsible for datatransport operation. Aspects include synchronizing frame transmissionwith the PHY layer, filling downlink allocations, or containers, withPDUs and fragmenting as necessary. The MAC common part sublayer 608schedules SDUs from upper layer bearer protocol modules into OFDM PHYallocations or containers. Aspects of the scheduler include:

1. The scheduler only needs to support two upper bearer protocols:

(a) Constant stream of broadcast data that uses a majority of thedownlink bandwidth. This bearer protocol does its own fragmentation toavoid the overhead of MAC layer fragmentation.

(b) A constant, but sparse, stream of SDUs that has highest priority,“steals” bandwidth from the other type of stream, and allows forMAC-layer fragmentation in some cases.

2. The scheduler does not form the transmit data frame structuredynamically. The frame structure is constant. The OFDM layout does notchange frame-by-frame, it remains constant for extremely long periods oftime, perhaps changing only when upgrades are made to the modulators.This is in contrast to a typical IEEE 802.16 device, where the scheduleris given control over the frame structure and PHY modulation and codingmodes.

3. The scheduler does not employ QoS functions. Service flow downlinkbandwidth requirements are dictated by a constant stream from the upperlayers.

FIG. 8 is a block diagram illustrated data flow through the MAC commonpart sublayer 608. As shown in FIG. 8, overhead messages 802 and contentdata, such as an MPEG-2 transport stream 804, are received at theconvergence sublayer 610. The overhead messages are processed by asignaling convergence protocol module 806 and the content data isprocessed by a content convergence protocol module 808. PDUs output fromthe signaling convergence protocol module 806 and the contentconvergence protocol module 808 are communicated to the schedule module614 in the MAC common part sublayer 612. The scheduler module 614processes the overhead and content PDUs and outputs combined PDUs to thexDU transformation protocol module 616. The output of the xDUtransformation module is communicated to the downlink traffic channelMAC module 644.

The xDU transformation protocol module 616 transforms MAC SDUs to PDUsthat are compatible with the IEEE 802.16 PDU (with generic MAC header(GMH)). The xDU transformation protocol module 616 includes thefollowing aspects.

1. It does not employ protocol procedures that are bidirectional. Forinstance, no registration, no basic capabilities negotiation, no DSx, noARQ, no uplink bandwidth grants, etc.

2. It does not pack multiple SDUs into a single PDU.

3. It supports SDU sizes up to largest PDU payload size, for example, upto 2041 bytes. In other words, an upper layer bearer protocol is notallowed to send an SDU that exceeds a predetermined upper limit, such as2041 bytes.

4. If necessary, the protocol module fragments SDUs into multiple PDUsto utilize OFDM PHY allocation regions. For example, in a typical casewhere a PDU “starts” in an allocation region, and its byte count wouldextend beyond the region, the protocol module fragments the PDU, placingthe first fragment in the current allocation and placing the otherfragment(s) in later allocations.

5. The protocol module supports static service flow establishment.Static means when another protocol (e.g., upper layer bearer protocol)establishes a service flow with the xDU transformation protocol module,it is immediately active, available and transitioned to a service flowactive state.

6. The xDU transformation protocol module does not generate or processMAP.

7. The xDU transformation protocol module on a base station maps SDUs toPDUs and then to allocation regions or HARQ packets such that the mobilestation (receiver) can extract PDUs and then SDUs in the same order.

8. The order of allocation regions is clarified so that both thefollowing conditions define allocation order:

-   -   (a) The order of their respective IEs in the MAP.    -   (b) The order of each allocation region's lowest symbol number.        And if two allocation regions have the lowest symbol number, the        allocation region with the lowest subchannel number is first.

9. The xDU transformation protocol module maps PDUs to an allocationregion accordingly and defines the mapping and the transmission order ofPDUs in an allocation region.

In a base station, a principle responsibility of the xDU transformationprotocol module is to take MAC-SDUs, generate MAC-PDUs with the properGMHs and fragmentation subheaders (if necessary), which are sized tofill OFDM allocation regions, or OFDM containers. In a mobile stationreceiver, the xDU transformation protocol module strips off the GMHs andperforms reassembly if necessary, thus forming SDUs. The xDUtransformation protocol module then demultiplexes SDUs (based on a CID)to the next upper layer bearer protocol (e.g., chooses the convergencesublayer).

MAC Control Sublayer

Following is further detail of the MAC control sublayer module, item 630in FIG. 6. The MAC control sublayer module 630 includes an air linkmanagement module 631 that operates in accordance with an air linkmanagement protocol. FIG. 9 is a state diagram illustrating aspects ofprocessing according to the air link management protocol by the air linkmanagement module, item 631 in FIG. 6, at a mobile station. The air linkmanagement protocol at the mobile station can be in one of 5 states: aninitialization state 902, a persistent state 904, a time slicing state906, scan state 908, and a handover state 910.

Upon entering the initialization state 902, the mobile station searchesa list of frequencies looking for a broadcast system. When a broadcastsystem is found, the initialization state enables the Shared SignalingMAC protocol (module 642 in FIG. 6) so that the MAP will be parsed intopublic data. The MAP information can be used to determine the serviceprovider and its own geographic region. The mobile station also usesthis information to refine its search list. When it is determined whichservice provider in the area is most acceptable, the mobile stationexits the initialization state 902 and the system enters the Persistentstate 904. If no service providers are found, the mobile stationperiodically repeats its frequency search until a satisfactory serviceprovided is found.

In the Persistent State 904, the mobile station is not time slicing onthe received signal. When the mobile station is not time slicing, allPDUs received by the Physical Layer Protocol will be passed to the MACsublayer. It is noted that in this state, because there is no timeslicing, the mobile station will be consuming considerably more powerthan in the Time-Slicing State 904, because the receiver is on toextract all PDUs. The persistent state 904 is needed for the upperlayers (the upper Data-Link Layer and Network Layer) to determine whatmulticast IP stream the application wishes to receive by examining theaggregate received stream (502 in FIG. 5). Once a desired IP stream, orstreams, are selected, then the Time Slicing State 904 can be entered toconserve power.

In the Time Slicing State 906, portions of the mobile station needed toreceive the broadcast data, referred to as the receiver, are switched onand off at appropriate times so as to receive and extract the desiredcontent streams from the aggregate stream, and to conserve power duringundesired content steams. The information needed to accomplish timeslicing is provided to this state via primitives from upper layers andfrom public data.

The Scan State 908 is entered from the Time Slicing State 906 under thecontrol of the Air-Link Management Protocol 631. The scan state 908 isentered into while the desired streams selected by upper layers are notbeing transmitted by the base station modulator, so as to not missapplication level data. In this state, the mobile station will scan foradjacent networks based upon information that is pre-programmed into themobile station and information that is received by the broadcast accessnetwork to which it is currently synchronized. In the scan state 908adjacent networks are evaluated as possible substitutes for the currentbroadcast system in the situation where signals from the currentbroadcast system are lost or deteriorate.

The Handover State 910 is entered into from the Time Slicing State 906when the signal of the current broadcast access network is either pooror non-existent. While in this state, broadcast access networks thatwere detected in the Scan state 908 (during “off” times of the TimeSlicing State 906) are examined for their suitability as a replacementfor the current network. If a suitable network is found, then thePersistent state 904 is re-entered, otherwise the Initialization state902 is re-entered. The Handover state 910 exists for the purpose ofrapidly acquiring a new network, rather than simply invoking theInitialization state 902, which typically will be slower in findingbroadcast access networks. If the Handover state 910 cannot rapidlyacquire a new network, then it invokes the Initialization state 902.

Initialization State 902

The air link management module 631, while in the initialization state902, operates an initialization state protocol at the mobile station toacquire a broadcast access service. FIG. 10 is a state diagramillustrating aspects of processing according to the initialization state902 of the air link management protocol.

The initialization state 902 implements a control protocol used at amobile station to acquire a signal from a broadcast access servicenetwork. Selection of a broadcast access network can be based on severalfactors. For example, in one embodiment, selection can be base on arecently used list (RUL) which is a cache table, or list, of recentlyused frequencies that the mobile station can use to search for abroadcast network. Selection can also be based on a full list of allpossible frequencies, and a preferred roaming list (PRL) this is basedon geo-location information. Using geo-location information can increasethe speed of the network selection process. For example, a table can beused to map a base station ID/network ID to a geo-location. Then, usinginformation in the broadcast signal, such as the base station ID ornetwork ID, a tailored preferred roaming list can be created.

The initialization state 902 protocol begins in an Inactive State 1002.This is the initial state of the protocol, where the protocol waits foran activate command. Upon receiving an activate command there is atransition to a recently used list (RUL) search state 1004. In the RULsearch state 1004, the protocol will attempt to acquire and synchronizeto a broadcast access service network by using a cached list, forexample a Recently Used List (RUL) of possible frequencies. The protocolwill leave this state under two conditions: a successful acquisition onone of the frequencies contained in the RUL; or none of the frequenciesin the RUL lead to acquisition.

In the HLL search state 1006, the protocol will use a highest likelihoodlist (HLL) to search for a broadcast access service network. Like theRUL Search State, the protocol can leave this state under a conditionwhere a network was found and under the condition that no broadcastaccess service network was found.

In an Out of Service Area State 1008, the protocol will sojourn for atime, waiting for another attempt at acquiring a broadcast network. Inthis state the Mobile Station need not operate its receiver, andtherefore should minimize its power consumption. The amount of timespent in this state will be a function of how the protocol transitionedinto this state. This Out of Service Area State 1008 should not beconfused with any other power save states that make up the sub-protocolsof the Default Air Link Management Protocol.

There is also a preferred roaming list (PRL) search state 1010. In thisstate, the protocol uses geo-location information obtained during theRUL or HLL, or both, to search a database for a preferred broadcastnetwork among a list of frequencies, thereby creating a preferredroaming list (PRL). The PRL can also be ordered in preference based uponvarious parameters such as cost, or other user preferences. Uponsuccessfully acquiring and synchronizing to a suitable broadcast accessservice network a transition from the PRL search state 1010 to aBroadcast Network Acquired State 1012 occurs. The database used for thePRL search can be included within a device by the manufacture, or it canbe downloaded to the device. In addition, the database can bemaintained, and updated during the life of the device.

Transition between the various states of the initialization state 902are now described. In the Inactive State 1002, the mobile station waitsto receive a command to activate it. Upon receipt of the command, theprotocol engages the Search Frequency List process using the RUL in theRUL Search State 1004. In the RUL Search State 1004, the protocol waitsfor the results of the Search Frequency List process. This process canconclude with one of two possible results. The process can return with ageo-location, indicating where the mobile is located geographically.This geo-location is used to index into the Preferred Roaming List (PRL)database. If there is an entry in the PRL database, the protocoltransitions to the PRL Search State 1010. If there is no entry in thePRL database for this geo-location, the protocol transitions to theInitialization Power Save State 1008. If the geo-location could not bedetermined using the RUL, then the protocol will again engage the SearchFrequency List process, this time with the Highest Likelihood List (HLL)as the argument. After this process is engaged, the protocol willtransition to the HLL Search State 1006.

The protocol sojourns in the HLL Search state 1006 awaiting the resultsof the Search Frequency List process. As in the RUL Search state 1004,the results of the Search Frequency List can indicate geo-location or nogeo-location. If geo-location is determined, the protocol seeks a PRL inthe PRL database. If one is found, the protocol engages the Search andAcquire process with the PRL as its argument in the PRL Search State1010. If no signal is found from within the frequencies contained in theHLL, the protocol transitions into the Initialization Power Save State1008.

The protocol sojourns in the PRL state 1010 while the Search and Acquireprocess is executing. If this process is successful, it returns with asignal indicating that a broadcast network was found within the PRL. Theprotocol state machine then transitions to the Broadcast NetworkAcquired State 1012. If no broadcast system was found within the PRL,this implies that a non-broadcast OFDM signal is present, which aided indetermining geo-location, however a broadcast system is not present.Under this condition the protocol transitions to the Out of Service AreaState 1008. In the Out of Service Area State 1008, the protocol will sitidle for a timed period (time period provided to this state from the“sending state”) then leave this state at the end of timed period. Theduration of the idle time period for this state is determined by thestate the protocol was in prior to entering the Out of Service AreaState 1008.

The protocol enters the Broadcast Network Acquired state 1012 once abroadcast signal is found within the PRL. The protocol will sojourn inthis state while certain tasks are executed. Tasks executed includeentering the center frequency, bandwidth, NAP ID, NSP ID, and NSPIdentifier Flag on which the mobile subscriber has found broadcastservice into the RUL, if it is not already present. Once the tasks arecomplete, the protocol will transition to the Inactive state.

The Recently Used List can be periodically purged of stale entries. Anentry becomes stale upon its expiry. The entry for the mobilesubscriber's home network has an expiry of infinity, and therefore willnever be purged.

The Search and Acquire process takes a frequency list and attemptspreamble acquisition and synchronization. A frequency list is providedto the process. Typically this frequency list is the PRL, however theprocess is not PRL specific. A frequency is chosen from the list,preamble is searched for and if found, a MAP detection is attempted.Ideally, when searching for a signal on a frequency that is known tocarry a broadcast signal, there should only be one preamble sequencedetected.

FIG. 11 is a block diagram illustrating an example of a base stationidentification (BSID) 1102. In this embodiment, the BSID 1102 includes aNetwork Access Provider/Network Service Provider (NAP/NSP) ID 1104, aNSP identifier flag 1106, an undefined region 1108, and a sector ID1110. The NAP ID 1104, the upper 24 bits of the BSID 1102, is comparedto the NAP ID of the frequency list entry. If the NAP ID 1104 matchesthe entry in the list, then the network is accepted. If the NAP ID 1104does not match the entry in the list, then the network is rejected.Another preamble index or another frequency is then chosen and thepreamble/MAP detection process is repeated.

In the event that the network access provider is different from thenetwork service provider, then the NSP ID 1104 is received and compared.Having a service provider(s) different from the network access provideris indicated by the most significant bit of the 24 least significantbits of the BSID. The NSP ID 1104 can be periodically broadcast in anoverhead message. If a mobile station requires NSP ID 1104 informationto match the information contained in the frequency list, and it doesnot, a new frequency is chosen. If no suitable network is found usingthe frequencies provided in the search list, the process will return tothe calling process.

Returning to FIG. 11, the upper 24 bits of the 48 bit BSID 1102 aredefined as a Network Access Provider (NAP) ID 1104. The NAP ID serves toidentify the owner and operator of the access network, that is who isoperating the access service network. The Network Service Provider (NSP)can be one or more providers of end-to-end service and such other thingsas accounting, authentication, security, etc. In some deployment cases,the network access provider can be the same as the network serviceprovider. This case is indicated in the BSID 1102 by the NSP identifierflag 1106 (the most significant bit of the 24 least significant bits ofthe BSID) being set to 0 (zero). Because of this case (called NAP+NSP),the format for the NAP ID 1004 and the NSP ID are identical. For thebroadcast system described herein, it is common for the NAP to be thesame as the NSP.

One of two possible formats, based upon the value of the 2 mostsignificant bits of the NSP ID 1104, are described. In one example, ifthe first two bits of the NSP ID 1122 read “00” then the remaining 22bits are simply a globally assigned identifier 1124, meaning that nobits are set aside specifically for geo-location. Geo-location wouldhave to be determined by a flat lookup table. If the first 2 bits of theNAP/ID read “11”, then the remaining 22 bits are divided according toITU-T Recommendation E.212 [ITU-T E.212], with the first 10 bitsdenoting the Mobile Country Code (MCC) 1126 and the final 12 bitsdenoting the Mobile Network Code (MNC) 1128. Coarse, country specific,geo-location can be arrived at by interpreting MCC 1126. The MNC 1128 isthen used to determine the access network operator.

The 23 least significant bits of the BSID are referred to as the NetworkElement Identifier (NE ID) 1130. These bits in combination with theNAP/NSP ID allow a mobile station to determine its geo-location once itreceives the BSID.

Persistent State 904

Returning to FIG. 9, the air link management module 631 transitions fromthe initialization state 902 to the persistent state 904. A moduleoperating in accordance with a persistent state protocol provides thecapability to a mobile station for monitoring the air link when nospecific traffic stream/program is yet selected to be received. Thepersistent state protocol allows a full unfiltered aggregate stream toarrive to layers above the convergence sublayer. This allows for upperdata link and network layer synchronization to the arriving packetstream without any receiver time slicing.

There is no module operating a persistent state protocol at a broadcastbase station. FIG. 12 is a state diagram illustrating operating statesfor a module operating in accordance with the persistent state protocol.As shown in FIG. 12, an inactive state 1202 is the initial state of theprotocol, where the protocol waits for the activate command. Uponreceiving an activate command, there is a transition to a monitor state1204. In the monitor state 1204 the mobile station monitors the downlinkchannels continually utilizing the DL Traffic MAC protocol. In thisstate the mobile station RF receiver circuitry is powered oncontinually. Upon receiving a deactivate command there is a transitionback to the inactive state 1202.

Time Slicing State 906

The air link management module 631 transitions from the persistent state904 to the time slicing state 906, as seen in FIG. 9. This protocol isapplicable only to a module in the mobile station and providesprocedures and messages used by the mobile station when it wishes toreceived a content traffic stream in a power efficient manner.

FIG. 13A is a state diagram illustrating aspects of processing accordingto the time slicing state 906. Beginning in an inactive state 1302, themodule operating in accordance with a time slicing protocol waits for anactivate command. Upon receiving an activate command there is atransition to an active state 1304. In the active state 1304 the mobilestation can receive traffic on the downlink data channel.

FIG. 13B is a state diagram illustrating sub-states within the activestate 1304. A first sub-state is the RF ON sub-state 1320. In the RF ONsub-state 1320, RF portions of the mobile station are activated whiledemodulation of received signals is ongoing. This corresponds to the ONtime of a time sliced burst of a particular service, such as item 512 inFIG. 5. At the end of the time slice ON interval, there is a transitionto an RF OFF state 1322. In the RF OFF state 1322, RF portions of themobile station are deactivated by, for example, removing or reducingpower to them. This corresponds to the OFF time of a time sliced burstor a particular service, such as item 514 in FIG. 5. When the start ofthe next time slice ON period is about to arrive, there is a transitionback to the RF ON state 1320.

While in the RF ON state 1320, a mobile station will activate modulesoperating with bearer protocols. In this state, the MS shall have the RFreceiver turned on and shall be capable of receiving the downlink datatraffic from the BS. The mobile station shall continue to receive thedownlink data traffic and send it on to the upper layers until the endof the time slice period is reached and the mobile station transitionsto the RF OFF state 1322.

In the RF OFF state 1322, the mobile station will deactivate modulesoperating bearer protocols and deactivate, or turn off, portions of itsRF to conserve battery power. While in this state, the mobile stationcontinues to process (send to the upper layers) the data that has beenreceived up to this point. The MS shall remain in this state until thenext time slice on period occurs, at which time there will be atransition to the RF ON state 1320. Based on a receiver implementation,the mobile station may need to turn on its receiver some amount of timebefore the beginning of the time slice on period in order to perform anysynchronization procedures that are required for the mobile station tosynchronize to the base station.

Scan State 908

Returning to FIG. 9, the air link management module 631 transitions fromthe time slicing state 906 to the scan state 908. A scan state module635 can implement a scan state protocol that seeks to exploit the timewhen the receiver's radio frequency (RF) components are otherwise off,during time slicing, to scan for adjacent broadcast networks. Areceiver's RF components are typically off during one of the sub-statesof the Time Slicing State protocol.

The scan state module implementing the scan state protocol will scan forbroadcast networks based upon information that is embedded in the mobilestation, such as, the preferred roaming list, and based upon informationthat is provided by the current broadcast access network, such as aNetwork Announced List (NAL).

This protocol will be activated and deactivated by the Default Air LinkManagement protocol implemented by air link management module 631 insuch a manner as to not interfere with the operation of the Time SlicingState module 634. As networks are found, the information relevant todescribing the found network is compiled in the Found Networks List(FNL). Maintenance of the FNL is the responsibility of this protocol. Ascan state module does not typically exist at the base station.

FIG. 14 is a state diagram illustrating aspects of processing accordingto the scan state 908. As shown in FIG. 14, the scan state module startsin an inactive state 1402 of the protocol where it waits for theactivate command. The scan state module then transitions to a scanningstate 1404 where the module will scan for adjacent networks.

Upon entering the scanning state 1404, the protocol will engage a ScanSearch Frequency List process. If a state exists from the previousactivation of this protocol, then the Scan Search Frequency List processwill engage using this state. Otherwise the Scan Search Frequency Listprocess will engage with the network announced list as its argument.

Once the NAL has been scanned, the Scan Search Frequency List process isre-engaged with the PRL as its argument. When both lists have beenscanned, the process is complete and the module transitions to theInactive state.

FIG. 15 is a flow diagram illustrating aspects of the scanning process.Flow begins in block 1502. In block 1504, a frequency is selected from alist of possible frequencies that may include a broadcast network. Flowcontinues to block 1506 and the selected frequency is scanned.Typically, the scanning process determines if a predefined preamblesignal is detected at the selected frequency, and if it is then a MAP isreceived.

Flow continues to block 1508 where the MAP is evaluated to determine ifthe found network is a broadcast network. Flow continues to block 1510and a found networks list is updated with broadcast networks that arefound. Flow then continues to block 1512 and stops.

Handover State 910

The air link management module 631 in FIG. 9 transitions from the timeslicing state 906 to the handover state 908. A handover state module 637can implement a handover state protocol that is entered into by themobile station upon losing connection with the current broadcast accessnetwork or the connection with the current broadcast network degradesbelow some acceptable measure of quality. This handover state protocolseeks to scan the frequencies contained in a Found Networks List (FNL)in an attempt to acquire an alternative broadcast access network. TheFNL is created and maintained by the scan state module 635.

This protocol is labeled as “Handover” however the events leading up tothe activation of this protocol and the actions taken by this protocoldo not accomplish handover in the classical cellular sense. The protocolexists for the purposes of rapidly acquiring a broadcast access network.The event that triggers this protocol is the loss of the currentbroadcast network, or the network connection degrades. This form ofhandover could be referred to as “hard hand-off.”

The handover module 647 at a mobile station can implement a handoverprotocol. FIG. 16 is a state diagram illustrating states of the handoverprotocol implemented by handover module 647. The handover module 647begins in an inactive state 1602 wherein the module waits for anactivate command. Upon receiving the activate command, the moduletransitions to a searching state 1604 where the module, in a mobilestation, will use entries of the found network list (FNL) identifiedduring previous scan states 635 to search for a suitable preamble. If asuitable preamble is found, indicating that a suitable broadcast networkis found, the new network is acquired and the module transitions back tothe inactive state 1602. If a suitable preamble is not found, indicatingthat a suitable broadcast network is not found, a handover acquisitionfailure is indicated and the module transitions back to the inactivestate 1602.

Overhead Message Module 636

The lower MAC control sublayer also includes an overhead message module636 that implements an overhead message protocol. The overhead messagemodule 636 can be implemented at the base station 112 of FIG. 1 or thesingle frequency network adapter 250 or base station 260 of FIG. 2.

In one embodiment, at a base station, the overhead message moduleimplements an overhead message protocol sending overhead messages to asignaling convergence protocol. In an embodiment, at a mobile station,the overhead message module implements an overhead message protocol toreceive overhead messages from a signaling convergence protocol. Theoverhead message modules also perform supervision on the overheadmessages necessary to keep the MAC Layer functioning. This modulepublishes the extracted information as Public Data for access by otherprotocols.

Examples of overhead messages include a Downlink Channel Descriptor(DCD) message and a System Identity Information-Advanced (SII-ADV)message.

These messages are unique, in that they pertain to multiple protocolsand are, therefore, specified separately. The overhead messages moduleimplements procedures related to transmission, reception and supervisionof these messages. This is a control protocol and the transmission unitof this protocol is a message. It does not carry payload on behalf ofother layers or protocols. This protocol uses the signaling convergenceprotocol to transmit and receive messages.

FIG. 17 is a state diagram illustrating the states of the overheadmessage protocol implemented by the overhead message module 636. In amobile station the overhead message module 636 begins in an inactivestate 1702. This is the initial state of the protocol, where theprotocol waits for the activate command. This state is only applicableto mobile station and occurs when mobile station has not acquired thebase station or is not required to receive the overhead messages.

In one embodiment, the Mobile Station overhead message module 636 willstart this protocol in the inactive state 1702, and the Base Stationoverhead message module 636 will start this protocol in the overheadmessages transmit/receive state 1704.

In one embodiment, the base station overhead message module 636 may addnew overhead messages. The mobile station overhead module 636 maydiscard overhead messages with a message ID field that it does notrecognize. In other embodiment, the base station overhead message module636 may add new fields to existing overhead messages. These fields canbe added to the end of the message.

When the mobile station overhead message module 636 is in the overheadmessages transmit/receive state 1704, it can start receiving overheadmessages and provide the contents of overhead messages as public data soas to make it available to the other MAC modules. When the base stationoverhead message module 636 is in the overhead message transmit/receivestate 1704, it can act as a transmitting conduit for overhead messagesfrom the associated lower MAC protocol.

MAC Sublayer

Following is further detail of one embodiment of the MAC sublayer module640 of FIG. 6. In this embodiment, the MAC sublayer 640 performsprocesses that can be implemented at various components in the system,such as, at the base station 112 and mobile station 106 of FIG. 1, orthe IP encapsulator 230, single frequency network adapter 230 basestation 260 or mobile station 270 of FIG. 2.

The MAC sublayer 640 includes a shared signaling MAC protocol module 642that implements a shared signaling MAC protocol. The shared signalingmodule is responsible for production (at the base station) andconsumption (at the mobile station) of the MAP PDU. This protocol is theonly protocol that directs the Physical Layer Protocol to send to (atthe base station) and receive from (at the mobile station) the MCH. Atthe mobile station, this protocol is responsible for supervision of theMAP PDU.

The MAC sublayer 640 also includes a downlink traffic channel MAC module644 that implements a downlink traffic channel MAC protocol. Thedownlink traffic channel MAC module 644 is responsible for directing thePhysical Layer Protocol to transmit (at the base station) and receive(at the mobile station) the DCH. At the base station, this protocoltakes a PDU train received from the xDU Transformation protocol andformulates a mega-PDU that exactly fits into the payload of the DCH. Atthe mobile station, this protocol will take this mega-PDU received viathe DCH and produce a train of PDUs for the xDU Transformation protocolthat is free of any Physical Layer padding.

Shared Signaling MAC Module 642

In one embodiment, the shared signaling MAC module 642 performs manyfunctions, including:

-   -   Defining the MAP PDU;    -   Mapping the MAP PDU to the MCH Physical Layer channel at the        base station; and    -   Controlling the Physical Layer at the mobile station so it will        receive the MCH and pass the MAP PDU to this protocol.

In one embodiment, the MAP PDU contains information necessary for theDownlink Traffic MAC protocol at the mobile station to control thePhysical Layer protocol. This information is received by this protocolat the mobile station and shared with the Downlink Traffic MAC protocol.The MAP PDU is mapped to the MCH. The MCH occupies the same location inthe broadcast physical layer frame. The MAP PDU originates at the basestation, and is received and interpreted by the mobile station.

At the base station, the composition of the MAP is governed by limitsplaced upon the size of the MCH and upon a scheduling entity which isnot defined by this air interface. This scheduling entity has networkwide scope, insuring that all base stations within a single frequencynetwork, will be generating exactly the same MAP

FIG. 18 is a state diagram illustrating the states of one embodiment ofthe shared signaling MAC module at the mobile station. At the basestation, this protocol is implemented with a single state, called theActive state. As shown in FIG. 18, the mobile station starts in aninactive state 1802. When the module receives an activate command ittransitions to an active state 1804, where it remains until receiving adeactivate command. In the active state 1804, the base station instanceof the shared signaling MAC module transmits and the instance of themodule at the mobile station receives the MAP PDU via the MCH physicallayer channel.

At the base station, the MAP PDU is mapped to the MCH. In oneembodiment, the MCH is transmitted using QPSK modulation, with a rate ½convolutional turbo coding. These requirements on the MCH imply that forthis channel, there are 6 data bytes per slot.

In one embodiment, the MCH can be transmitted in the first symbol groupof the Physical Layer Frame, which is a PUSC zone. The MCH will onlyoccupy the remainder of the first symbol group and will not spill overinto the second symbol group. This requirement places a restriction onthe size, in sub-channels, of the MCH. This restricted size will dependupon the size of the FFT. There is an optional zone switch after thefirst symbol group.

In one embodiment, the Physical Layer channel described by the MAP canbe the DCH. The DCH can employ either convolutional coding orconvolutional Turbo coding. The DCH can use convolutional Turbo codingwith incremental redundancy (IR). The DCH can commence on the first slotof the second symbol group and encompass the remainder of the PhysicalLayer Frame. The zone type of the DCH can be either PUSC or PUSC with ⅔antenna space time coding (STC). If the zone type is ⅔ antenna STC, thisimplies a zone switch after the first symbol group.

In one embodiment, the fundamental parameters of the Physical Layerwaveform and the resulting symbol durations with cyclic prefix, G, beingboth ¼ and ⅛. Using appropriate symbol times, the number of symbols perframe and the receive-receive gap (TRrg) can be computed, using thefollowing rules for determining TRrg.

-   -   1. TRrg is what remains after the maximum integral number of        symbols that would fit into TTddFrame have been subtracted from        TTddFrame    -   2. If TRrg is less that 45 microseconds, then TRrg is        incremented by one symbol duration, and the number of symbols        per TTddFrame is decremented by one.

In an embodiment, a receive-receive gap can be added to the broadcast toallow for frame synchronization techniques that rely on a gap betweencyclic prefix detections exceeding a symbol duration. In one example,the receive-receive gap may be no less than 45 microseconds because thisrepresents roughly 50% of a symbol duration, and therefore could producea strong enough signature in a cyclic prefix gap detection algorithm.

In one embodiment, a H-ARQ is employed at the Physical Layer where theremay be a single H-ARQ region within the DCH encompassing the entire DCH.Within this H-ARQ region, there may exist multiple sub-bursts. Thenumber of slots occupied by each sub-burst can vary. The total size ofthe H-ARQ region, and hence the DCH, will depend upon the size of theFFT. The DCH begins on the first symbol following the first symbol group(the first symbol group contains the FCH and the MCH). In one example,the DCH begins on symbol number 3, with the preamble occupying symbolnumber 0, and the FCH and the MCH occupying symbols 1 and 2.

Typically, each H-ARQ sub-burst carries one H-ARQ packet. In oneembodiment, the size of this packet can vary according to the set: {48,96, 144, 192, 288, 384, 480, 960, 1920, 2880, 3840, 4800, 9600, 14400,19200, 24000}. If the H-ARQ packet size is chosen to be large, thenfewer sub-bursts are required to fill the entire DCH. If the H-ARQpacket size is chosen to be small, then more sub-bursts are required tofill the entire DCH.

Downlink Traffic Channel MAC Module

The downlink traffic channel MAC module 644 maps downlink MAC PDUsreceived from the xDU Transformation module 616 to the physical layerchannel (F-DCH) at the Base Station. At the mobile station the xDUtransformation module 616 s protocol provides capability to extractdownlink MAC PDUs from the physical layer channel (F-DCH), and processesthem for reception. The module processes all the MAC PDUs including MACmanagement PDUs as well as applications PDUs.

FIG. 19 is a state diagram illustrating states of the downlink trafficchannel MAC module 644. The module in the mobile station begins in aninactive state 1902, where the module waits for an activate command.This state is only applicable to mobile station and occurs when mobilestation is not required to receive the downlink traffic. Upon receivingan activate command, the module transitions to a PDU transmit/receivestate 1904. In the PDU transmit/receive state 1904 the base stationtransmits the PDU with fixed/variable length. In this state the mobilestation receives the PDU with fixed/variable length.

The mobile station enters the PDU transmit/receive state 1904 uponreceiving the activate command. When the Mobile Station is in the PDUtransmit/receive state 1904, it can start receiving PDUs from thePhysical Layer Protocol from F-DCH and can start passing the PDU to thexDU transformation module 616 in the mobile station. When in the PDUtransmit/receive state 1904, the mobile station can monitor the PDUsreceived from the physical layer protocol 662 and indicate a failure ifno PDU is received for a significant interval. The mobile station canexit the PDU transmit/receive state 1904 upon receiving a deactivatecommand, when it will transition to the inactive state 1902.

When the Base Station is in the PDU transmit/receive state 1904 it canstart receiving PDUs from the xDU transformation module 616 and startpassing the PDUs to the F-DCH of Physical Layer Protocol.

Physical Layer Control Sublayer

Following is further detail of the physical layer control sublayermodule 650 of FIG. 6. The physical layer control sublayer includes aphysical layer control module 652 that implements a physical layercontrol protocol. In one embodiment, the physical layer control module652 can be implemented on the transmit side in the base station 112 ofFIG. 1 or the single frequency network adapter 520 or base station 620of FIG. 2. In an embodiment, the physical layer control module 652 maybe implemented in a receiver in the mobile station 106 of FIG. 1 or themobile station 270 of FIG. 2.

The physical layer control module 652 provides the physical layercontrol procedures for the base station and the mobile station. FIG. 20is a state diagram illustrating the states of the physical layer controlmodule. The module begins in an inactive state 2002. In the inactivestate, the module waits for an activate command. Upon receiving anactivate command the module transitions to an active state 2004. In theactive state 2004 the base station transmits the FCH on the downlink andthe mobile station receives and decodes the FCH. When the MS receives aninactivate command, while in the Active state, it transitions to theinactive state 2002.

In the active state 2004, the base station can transmit the FCH at thebeginning (right after the downlink) of each downlink frame. The FCHcarries the DL frame prefix, which is a data structure containinginformation regarding the current frame. The DL frame prefix includes asubchannel bitmap indicating which groups of subchannel are used on thefirst PUSC zone and on PUSC zones in which use all subchannels indicatoris set to ‘0,’ meaning not used by this segment.

In one embodiment, the DL frame prefix also includes a repetition codingindication that indicates the repetition code used for the MAP.Repetition code may be 0 (no additional repetition), 1 (one additionalrepetition), 2 (three additional repetition) or 3 (five additionalrepetitions). The DL frame prefix also includes a coding indication thatindicates the FEC encoding used for the MAP. The MAP shall betransmitted with QPSK modulation at FEC rate ½. The BS shall ensure thatMAP is sent with the mandatory coding scheme often enough to ensureuninterrupted operation of a subscriber station (SS) supporting only themandatory coding scheme. In addition, the DL frame prefix includes a Maplength value that defines the length, in slots, of the MAP message thatfollows immediately after the DL frame prefix after repetition coding isapplied. In one embodiment, before being mapped to the FCH, the 24-bitDL frame prefix shall be duplicated to form a 48-bit block which is theminimal FEC block size.

In an embodiment, in a PUSC, any segment can be allocated at least thesame amount of subchannels as in a subchannel group #0. For FFT sizesother than 128, the first 4 slots in the downlink part of the segmentcontain the FCH. These slots contain 48 bits modulated by QPSK withcoding rate ½ and repetition coding of 4. For FFT size 128, the firstslot in the downlink part of the segment is dedicated to FCH andrepetition is not applied. The basic allocated subchannel sets forSegments 0, 1, and 2 are Subchannel group #0, #2 and #4 respectively.

In one embodiment, the mobile station can be capable of receiving anddecoding the FCH that is sent by the base station at the beginning ofeach frame. If the two DL frame prefix messages received in the FCH donot match, then the mobile station can generate a FCH DL Frame PrefixFCH DL Frame Prefix indication and can wait for the next downlink frame.After successful decoding of the DL Frame Prefix message in the FCH(there is no mismatch between the two DL Frame Prefix received in theFCH), the MS can have the knowledge of how many and which subchannelsare allocated to the PUSC segment.

In one embodiment, to observe the allocation of the subchannels in thedownlink as a contiguous allocation block, the subchannel can berenumbered. The renumbering for the first PUSC zone can start form theFCH subchannels (renumbered to values 0 . . . 11), then continuenumbering the subchannels in a cyclic manner to the last allocatedsubchannel and from the first allocated subchannel to the FCHsubchannels.

In another embodiment, for PUSC zones in which the “use all SC”indicator is set to ‘1’ or which are defined by AAS_DL_IE( ),renumbering can be performed starting from subchannel(Nsubchannels/3)*PRBS_ID,. where PRBS_ID is specified in theSTC_DL_Zone_IE or AAS_DL_IE( ). For other PUSC zones, in which the “useall SC” indicator is set to ‘0’, the renumbering shall be the same as inthe first PUSC zone.

In one embodiment, the mobile station can be capable of determining thatthe System Time has to be corrected because of the drift in timingexperienced at the receiver. Once it has been determined that a timingcorrection has to be applied to the SystemTime, the mobile station canupdate the global public parameter System Time Correction and generatethe System Time Correction Parameter Updated Indication.

In an embodiment, once the mobile station has achieved downlinksynchronization, it can continue to be in sync until one of thefollowing events occurs:

-   -   No valid MAP message has been received for Lost_MAP_Interval, or    -   T1 interval has elapsed without a valid DCD.

When one of the above events occurs, the MS can declare a loss ofsynchronization and generate a DL Synchronization-Lost Indication.

Physical Layer Sublayer

Following is further detail of the physical layer sublayer module 660 ofFIG. 6. The physical layer sublayer includes a physical layer module 662that implements a physical layer protocol. In one embodiment, thephysical layer control module 652 can be implemented on the transmitside in the base station 112 of FIG. 1 or the single frequency networkadapter 520 or base station 620 of FIG. 2. In an embodiment, thephysical layer module may be implemented in a receiver in the mobilestation 106 of FIG. 1 or the mobile station 270 of FIG. 2.

The physical layer is a broadcast only layer. Implementation of thephysical layer is fundamentally simpler because it is downlink only anddoes not need to support any uplink transmissions. In one embodiment,the layer uses fixed modulation and coding chosen to maximize coveragewithout ARQ mechanisms. Multiple access aspects of OFDM are notemployed, as all mobile stations potentially receive the same broadcastsignal or programming. Without an uplink there is no duplexing, so theOFDM TDD frame structure reduces to an OFDM TD frame structure that doesnot schedule reverse link transmissions.

In one embodiment, the frame of the physical layer will be either 5, 10,or 20 milliseconds in length. The permutation type is PUSC. The firstsymbol of the frame will be a preamble, selected from among the 114available preamble sequences. This preamble sequence will not change andwill be common to all modulators. The next two symbols (first symbolgroup) will contain the FCH and MAP. At the conclusion of the firstsymbol group, an optional zone switch will occur. This zone switch willallow for optional STC PUSC. The remainder of the frame consists of onelarge allocation. This allocation will contain MAC PDUs channel codedwith either CTC or CTC IR H-ARQ with no acknowledgement.

FIG. 21 is a flow diagram of one embodiment of a method of broadcastingdata. Flow begins in block 2102 where a stream of content is received.In one embodiment, multiple streams of content are received. The contentcan be, for example, movies, games, audio broadcast, broadcasttelevision programs, or other multimedia data. Flow continues to block2104 where the received content is encapsulated into an IP/MAC contentstream.

Flow continues to block 2106 where the encapsulated content stream isbroadcast from a plurality of transmitters. The transmitters aresynchronized, and are configured to transmit the same signal from theplurality of transmitters. Flow continues to block 2102 and the processof receiving, encapsulating, and broadcasting continues.

FIG. 22 is a flow diagram of an embodiment for receiving broadcast datain a single frequency network having a plurality of transmitters. Flowbegins in block 2202 where a receiver scans pre-selected frequenciessearching for and acquiring preambles from OFDM signals. When a preamblehas been acquired flow continues to block 2204 where it is determined ifthe OFDM signal is a broadcast signal. For example, a MAP in the OFDMsignal can be examined to determine if the signal is a broadcast signal.

If the signal is a broadcast signal, flow continues to block 2206 andthe receiver synchronizes to the broadcast signal. Once synchronized,flow continues to block 2208 and an aggregate content stream isreceived. The aggregate content stream includes a plurality ofindividual IP streams that have been encapsulated. Flow continues toblock 2210 where at least one of the individual IP streams is extractedfrom the aggregate stream.

FIG. 23 is a block diagram of an embodiment of a receiver 2301 in abroadcast system according to the invention. The receiver includes anantenna 2302 that communicates RF signals to a receiver 2304. Thereceiver 2304 is configured to receive an RF broadcast signal,demodulate it and provide a baseband signal to a processor 2306.

The processor 2306 receives the baseband data that includes a compositestream of content and the processor 2306 extracts a desired IP streamfrom the composite stream. In one embodiment, the processor 2306processes the extracted IP stream and presents it to a user. In anotherembodiment, the processor 2306 communicates the extracted IP stream toan optional rendering engine 2308 and the rendering engine 2308processes the IP stream and presents it to the user. The receiver 2301also includes a memory 2310. The memory 2310 can be used by theprocessor 2306 and the rendering engine 2308 (if included) for storageof data during operation. In addition, the memory 2310 may includeinstructions used by the processor 2306 and rendering engine 2308 duringoperation.

It is noted that modules, or components, of the receiver 2301 can beseparated. For example, the antenna 2302 can be located separately fromthe receiver 2304 and the processor 2306. Likewise, the rendering engine2308 can be located separately from the processor 2306. Othercombinations are also possible.

FIG. 24 is a block diagram of an embodiment of a transmitter 2401 in abroadcast system. The transmitter 2401 includes a network interface 2402adapted to receive content from an IP network. In one embodiment thereis a single content stream received at the network interface 2402, inother embodiments there are a plurality of content streams received atthe network interface 2402. The network interface 2402 communicates thereceived content to a processor 2404. The processor 2404 encapsulatesthe content into an IP/MAC content stream.

The processor 2404 communicates the encapsulated content to atransmitter 2406. The transmitter 2406 is configured to transmit thecontent as an OFDM signal via antenna 2408. In one embodiment, thetransmission of the content by the transmitter 2401 is synchronized withthe transmission of the same content by other transmitters within asingle frequency network.

The transmitter 2401 also includes a memory 2410. The memory 2410 can beused by the processor 2404 for storage of data during operation. Inaddition, the memory 2410 may include instructions used by the processor2404 during operation.

The various modules and components of the transmitter 2401 can beseparated. For example, the antenna 2408 can be separated from thetransmitter 2406. In another example, the antenna 2408 and transmitter2406 are located separately from the processor 2404, memory 2410, andnetwork interface 2402. Other combinations are also possible.

FIG. 25 is a flow diagram of an embodiment of a method for assigning aconnection identifier to a plurality of IP content streams in abroadcast system of the present invention. Flow begins in block 2502where a plurality of IP content streams are received. Flow continues toblock 2504 where the plurality of IP content streams are interleavedinto an aggregate content stream.

Flow continues to block 2506 where a unique connection identifier isassigned to the aggregate content stream. Then, in block 2508, theaggregate content stream is transmitted synchronously from a pluralityof transmitters within a single frequency network.

FIG. 26 is a flow diagram of another embodiment of a method forassigning a connection identifier to a plurality of IP content streamsin a broadcast system of the present invention. Flow begins in block2602 where a plurality of IP content streams are received. Flowcontinues to block 2604 where the plurality of IP content streams areinterleaved into an aggregate content stream.

Flow continues to block 2608 where a unique connection identifier isassigned to each individual IP stream within the aggregate contentstream. Then, in block 2608, the aggregate content stream is transmittedsynchronously from a plurality of transmitters within a single frequencynetwork.

FIG. 27 is a flow diagram of an embodiment of a method of managing awireless communication link in a broadcast system of the presentinvention. Flow begins in block 2702 where a receiver in the broadcastsystem is initialized. Flow continues to block 2703 where a channel ofthe communication link is selected. Then in block 2704 the receiveracquires a communication signal. In one embodiment, the received signalis an OFDM signal and receiving the signal includes acquiring apreamble, and detecting a downlink map in the OFDM signal. Flowcontinues to block 2706 where the signal received is analyzed todetermine if it is a broadcast signal. In one embodiment, the downlinkmap of the signal is analyzed. Flow continues to block 2708 in which itis determined if the received signal is a broadcast signal.

If the received signal is not a broadcast signal flow continues to block2703 and another channel is selected and communication signals areacquired. If, in block 2708, it is determined that the received signalis a broadcast signal, then flow continues to block 2710 and thereceiver begins receiving content from the broadcast system. In oneembodiment, the receiver receives content from the broadcast system withthe receiver operating in a time slicing mode.

FIG. 28 is a flow diagram of another embodiment of a method of managinga wireless communication link in a broadcast system of the presentinvention. Flow begins in block 2802 where a receiver acquires a signalfrom a broadcast network. Flow continues to block 2804 where thereceiver receives content from the broadcast network. In block 2804 thereceiver is operating in a time slice mode where the receiver acquiresthe broadcast signal when desired content is being broadcast by thesystem (time slice on) and does not acquire the broadcast signal whendesired content is not being broadcast (time slice off).

Flow continues to block 2806 where it is determined if the receiver isoperating in a time slice off period. If the receiver is not in a timeslice off period, meaning that it is in a time slice on period, flowreturns to block 2804 and the receiver continues to receive content.Returning to block 2806, if the receiver is in a time slice off periodflow continues to block 2808 where adjacent networks are scanned todetermine if they are broadcast networks, and to determine the qualityof the signal received from adjacent broadcast networks. In block 2810the scan results are saved.

Flow continues to block 2812 where it is determined if the receiver isentering a time slice on period. If the receiver is not entering a timeslice on period, flow returns to block 2808 and the receiver can scanfor additional networks or perform other operations, or enter a sleepstate. If the receiver is entering a time slice on period flow returnsto block 2804 and the receiver receives content.

FIG. 29 is a flow diagram of another embodiment of a method of managinga wireless communication link in a broadcast system of the presentinvention. In block 2902 content is received. Flow continues to block2904 and the current network is evaluated. In one embodiment, theevaluation of the current network is to determine if the operation ofthe current network is satisfactory, for example, if the network hassufficient signal to noise ratio, or bit error rate, or other networkperformance metric.

Flow continues to block 2906 where it is determined if the currentnetwork is satisfactory. If the current network is satisfactory, flowreturns to block 2902 and additional content is received. If, in block2906, it is determined that the current network is not satisfactory thenflow continues to block 2908 and a handover to a new network isperformed. In one embodiment, the new network is selected from a list ofsatisfactory networks identified during a scan of adjacent networks.

The above description of the disclosed embodiments is provided to enableany person skilled in the art to make or use the invention. Numerousmodifications to these embodiments would be readily apparent to thoseskilled in the art, and the principals defined herein can be applied toother embodiments without departing from the spirit or scope of theinvention. Thus, the invention is not intended to be limited to theembodiments shown herein but is to be accorded the widest scopeconsistent with the principal and novel features disclosed herein.

Various implementations of the invention are realized in electronichardware, computer software, or combinations of these technologies. Someimplementations include one or more computer programs executed by one ormore computing devices. For example, in one implementation, the methodfor monitoring and/or converting the status, running diagnostics, andotherwise providing functions related to status and management of thewireless communication device includes one or more computers executingsoftware implementing the monitoring and management functions. Ingeneral, each computer includes one or more processors, one or moredata-storage components (e.g., volatile or non-volatile memory modulesand persistent optical and magnetic storage devices, such as hard andfloppy disk drives, CD-ROM drives, and magnetic tape drives), one ormore input devices (e.g., mice and keyboards), and one or more outputdevices (e.g., display consoles and printers).

The computer programs include executable code that is usually stored ina persistent storage medium and then copied into memory at run-time. Atleast one processor executes the code by retrieving program instructionsfrom memory in a prescribed order. When executing the program code, thecomputer receives data from the input and/or storage devices, performsoperations on the data, and then delivers the resulting data to theoutput and/or storage devices.

Various illustrative implementations of the present invention have beendescribed. However, one of ordinary skill in the art will see thatadditional implementations are also possible and within the scope of thepresent invention.

Accordingly, the present invention is not limited to only thoseimplementations described above. Those of skill in the art willappreciate that the various illustrative modules and method stepsdescribed in connection with the above described figures and theimplementations disclosed herein can often be implemented as electronichardware, software, firmware or combinations of the foregoing. Toclearly illustrate this interchangeability of hardware and software,various illustrative modules and method steps have been described abovegenerally in terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.Skilled persons can implement the described functionality in varyingways for each particular application, but such implementation decisionsshould not be interpreted as causing a departure from the scope of theinvention. In addition, the grouping of functions within a module orstep is for ease of description. Specific functions can be moved fromone module or step to another without departing from the invention.

Moreover, the various illustrative modules and method steps described inconnection with the implementations disclosed herein can be implementedor performed with a general purpose processor, a digital signalprocessor (“DSP”), an application specific integrated circuit (“ASIC”),a field programmable gate array (“FPGA”) or other programmable logicdevice, discrete gate or transistor logic, discrete hardware components,or any combination thereof designed to perform the functions describedherein. A general-purpose processor can be a microprocessor, but in thealternative, the processor can be any processor, controller,microcontroller, or state machine. A processor can also be implementedas a combination of computing devices, for example, a combination of aDSP and a microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

Additionally, the steps of a method or algorithm described in connectionwith the implementations disclosed herein can be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module can reside in RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, harddisk, a removable disk, a CD-ROM, or any other form of storage mediumincluding a network storage medium. An exemplary storage medium can becoupled to the processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium can be integral to the processor. The processor andthe storage medium can also reside in an ASIC.

The above description of the disclosed implementations is provided toenable any person skilled in the art to make or use the invention.Various modifications to these implementations will be readily apparentto those skilled in the art, and the generic principles described hereincan be applied to other implementations without departing from thespirit or scope of the invention. Thus, it is to be understood that thedescription and drawings presented herein represent exampleimplementations of the invention and are therefore representative of thesubject matter which is broadly contemplated by the present invention.It is further understood that the scope of the present invention fullyencompasses other implementations and that the scope of the presentinvention is accordingly limited by nothing other than the appendedclaims.

1. A method of maintaining signal reception in a wireless broadcastnetwork, the method comprising: receiving an identical orthogonalfrequency division multiplexed (OFDM) signal from a first transmitter ofa plurality of transmitters in the wireless broadcast network, theplurality of transmitters configured to simultaneously transmit theidentical OFDM signal; synchronizing to the identical OFDM signal; andreceiving the identical OFDM signal from a second transmitter of theplurality of transmitters while maintaining synchronization with theidentical OFDM signal.
 2. The method of claim 1, wherein the wirelessbroadcast network is a single frequency network and the plurality oftransmitters are synchronized with respect to each other.
 3. The methodof claim 1, wherein the identical OFDM signal comprises a plurality ofindividual content data streams that are combined into an aggregate datastream.
 4. The method of claim 3, wherein the identical OFDM signalincludes one connection identification value associated with the entireaggregate data stream.
 5. The method of claim 3, wherein the identicalOFDM signal includes a unique connection identification value associatedwith each individual content data stream in the aggregate data stream.6. The method of claim 3, wherein the plurality of individual contentstreams comprise IP content.
 7. The method of claim 1, furthercomprising simultaneously receiving the identical OFDM signal from aplurality of transmitters and maintaining synchronization with theidentical OFDM signal.
 8. The method of claim 1, wherein the identicalOFDM signal is simultaneously received from both the first transmitterand the second transmitter for a time period and, at the expiration ofthe time period, the identical OFDM signal is received from only thesecond transmitter while synchronization to the identical OFDM signal ismaintained.
 9. A receiver comprising: a receiving module adapted toreceive orthogonal frequency division multiplexed (OFDM) signals from aplurality of transmitters in a wireless broadcast network, the pluralityof transmitters configured to simultaneously transmit an identical OFDMsignal; and a processor configured to synchronize to the identical OFDMsignal received by the receiving module from a first transmitter of theplurality of transmitters, and to maintain synchronization with theidentical OFDM signal while the receiving module receives the identicalOFDM signal from a second transmitter of the plurality of transmitters.10. The receiver of claim 9, wherein the identical OFDM signal comprisesan aggregate content stream comprised of a plurality of individualcontent streams.
 11. The receiver of claim 10, wherein the identicalOFDM signal includes at least one connection identification value. 12.The receiver of claim 11, wherein only one connection identificationvalue is associated with the aggregate content stream.
 13. The receiverof claim 11, wherein a unique connection identification value isassociated with each of the individual content streams in the aggregatecontent stream.
 14. The receiver of claim 9, wherein the identical OFDMsignal includes a base station identification.
 15. The receiver of claim9, wherein the receiver module simultaneously receives the identicalOFDM signal from a plurality of transmitters while synchronization withthe identical OFDM signal is maintained.
 16. The receiver of claim 9,wherein the identical OFDM signal is simultaneously received by thereceiver module from both the first transmitter and the secondtransmitter for a time period and, at the expiration of the time period,the identical OFDM signal is received by the receiver module from onlythe second transmitter while synchronization to the identical OFDMsignal is maintained.
 17. The receiver of claim 9, wherein the wirelessbroadcast network is a single frequency network and the plurality oftransmitters are synchronized with respect to each other
 18. A networkcomprising: a single frequency network adapter configured to receiveencapsulated transport stream packets and to format the transport streampackets into service data units; a plurality of transmitters configuredto receive the service data units and to synchronously transmit theservice data units such that each of the plurality of transmittersbroadcasts an identical signal; and at least one receiver configured tosynchronize to the identical signal received from a first transmitter ofthe plurality of transmitters, and to receive the identical signal froma second transmitter of the plurality of transmitters while maintainingsynchronization with the identical signal.
 19. The network of claim 18,wherein the signal received is an orthogonal frequency divisionmultiplexed (OFDM) signal.
 20. A method of broadcasting comprising:receiving encapsulated transport stream packets and formatting thetransport stream packets into service data units; synchronouslytransmitting the service data units from a plurality of transmitterssuch that each of the plurality of transmitters simultaneouslybroadcasts an identical signal; receiving the identical signal from afirst transmitter of the plurality of transmitters; synchronizing to theidentical signal received from the first transmitter; and receiving theidentical signal from a second first transmitter of the plurality oftransmitters while maintaining synchronization with the identicalsignal.
 21. The network of claim 20, wherein the identical signalcomprises an orthogonal frequency division multiplexed (OFDM) signal.22. One or more computer readable media storing computer executableinstructions that, when executed perform a method comprising: receivingan identical orthogonal frequency division multiplexed (OFDM) signalfrom a first transmitter of a plurality of transmitters in a wirelessbroadcast network, the plurality of transmitters configured tosimultaneously transmit the identical OFDM signal; synchronizing to theidentical OFDM signal; and receiving the identical OFDM signal from asecond transmitter of the plurality of transmitters while maintainingsynchronization with the identical OFDM signal.